This invention relates generally to tufting machines for forming cut pile fabric and more particularly to improved knife blocks for mounting the knives in such machines.
In tufting machines in which at least some of the tufts are cut, an oscillating knife cooperates with an oscillating hook or looper to cut the loop of yarn that has been seized by the looper from a corresponding needle. It is conventional in such machines for the knife to be supported and retained in a knife block carried by an oscillating knife bar. Examples of the known knife blocks are illustrated in Card U.S. Pat. No. 3,277,852; Cobble et al U.S. Pat. No. 3,386,398; Cobble U.S. Pat. No. 3,604,379; Wear U.S. Pat. No. 4,009,669 and British Pat. No. 1,309,961. Each of these patents discloses a knife block limited to mounting two or more conventionally aligned knives to cooperate with respective cooperating hooks having aligned throats. It is known, however, to produce a finer gauge of pile fabric by providing a tufting machine with parallel rows of staggered needles. In such machines the hooks which cooperate with adjacent offset needles may either have hooks with aligned throats, as illustrated in Crumbliss et al U.S. Pat. No. 3,913,505; Card U.S. Pat. No. 4,003,321 and Short U.S. Pat. No. 4,067,270; or the hooks may have throats offset by an amount substantially equal to that of the stagger, as illustrated in Card U.S. Pat. No. 3,084,644; Woodcock U.S. Pat. No. 3,440,983 and British Pat. No. 1,438,173. When the throats of the hooks are aligned the knives, which cut at the throats, are also aligned and conventional type knife blocks are adaptable. However, when the throats of adjacent hooks are offset, so too must be the knives and the knife receiving channels of multi-knife mounting blocks.
The use of said screws acting directly on the edges of the knives was previously discarded by the prior art because of the many difficulties presented. As illustrated in the aforesaid patents various constructions have been proposed for securing the knives within the knife block channels of blocks carrying aligned knives. These proposals use various forms and arrangements of clamping members which act on the rear edges of two of the knives. Many of these constructions require extensive machine work in the formation of the block and the formation of the clamping member. Moreover, in those tufting machines having non-aligned knives these prior art proposals are inapplicable because the rear edge of the knives are non-aligned.